Glass substrate, semiconductor device, and display device

ABSTRACT

A glass substrate has a compaction of 0.1 to 100 ppm. An absolute value |Δα50/100| of a difference between an average coefficient of thermal expansion α50/100 of the glass substrate and an average coefficient of thermal expansion of single-crystal silicon at 50° C. to 100° C., an absolute value |Δα100/200| of a difference between an average coefficient of thermal expansion α100/200 of the glass substrate and an average coefficient of thermal expansion of the single-crystal silicon at 100° C. to 200° C., and an absolute value |Δα200/300| of a difference between an average coefficient of thermal expansion α200/300 of the glass substrate and an average coefficient of thermal expansion of the single-crystal silicon at 200° C. to 300° C. are 0.16 ppm/° C. or less.

TECHNICAL FIELD

The present invention relates to a glass substrate, a semiconductordevice, and a display device.

BACKGROUND ART

In recent years, video technology such as VR (Virtual Reality) or AR(Augmented Reality) has been developed, and the market in this field isexpected to expand in the future. At the same time, it is requested toachieve higher resolution in a display device in order to obtain ahigher sense of immersion in a video image. However, a display devicesuch as an eyepiece display (near-eye display) generally used in thisfield has an extremely small display size. Therefore, in order to obtainan ultrahigh-definition display, it is expected to require very highimage resolution, for example, a value of 1,000 ppi, 2,000 ppi orhigher.

However, with miniaturization of a TFT (Thin-Film Transistor) element,there is a problem that a problem of a variation in TFT performance iscaused by a problem of a grain boundary in LTPS (Low-TemperaturePoly-Silicon) used in the background art. On the other hand, amorphoussilicon having no grain boundary has a problem that the mobility is low.In the present situation, it is difficult to put amorphous silicon intopractical use.

In consideration of the aforementioned circumstances, there is atechnique in which a control TFT is formed on a single-crystal siliconwafer, and laminated to a glass substrate, and only a device part isthen separated and transferred to the glass substrate. According to thismethod, since single-crystal silicon is used for TFT, it is possible tosolve the problem as to the low mobility and the variation in TFTproperties.

CITATION LIST Patent Literature

Patent Literature 1: JP-A-2007-220749

SUMMARY OF THE INVENTION Problem that the Invention is to Solve

Such an ultrahigh-definition display is manufactured through variousprocesses such as a step of laminating a glass substrate and a siliconwafer on each other under a temperature of about 200-700° C., a step ofperforming heat treatment (such as activation heat treatment) after thelaminating step, a step of performing chemical treatment, and a step offorming a display element after forming a TFT. Alkali-free glass isrequired in this method. However, use of alkali-free glass in thebackground art causes problems. For example, the glass warps due to adifference in coefficient of thermal expansion between the glass and thesilicon wafer when the both are laminated to each other; a patterndeviates due to thermal shrinkage of the glass substrate during the heattreatment; and the glass substrate is clouded by the chemical treatment.No technique that can solve these problems has been implemented.

One embodiment of the invention provides a glass substrate suitable formanufacturing a small-size and high-definition display device, and alsoprovides a semiconductor device and a display device in which the glasssubstrate has been laminated.

Means for Solving the Problem

A glass substrate according to one embodiment of the invention is aglass substrate having a compaction of 0.1 to 100 ppm, wherein anabsolute value |Δα_(50/100)| of a difference between an averagecoefficient of thermal expansion α_(50/100) of the glass substrate andan average coefficient of thermal expansion of single-crystal silicon at50° C. to 100° C., an absolute value |Δα_(100/200)| of a differencebetween an average coefficient of thermal expansion α_(100/200) of theglass substrate and an average coefficient of thermal expansion of thesingle-crystal silicon at 100° C. to 200° C., and an absolute value|Δα_(200/300)| of a difference between an average coefficient of thermalexpansion α_(200/300) of the glass substrate and an average coefficientof thermal expansion of the single-crystal silicon at 200° C. to 300° C.are 0.16 ppm/° C. or less.

A semiconductor device according to one embodiment of the inventionincludes a glass substrate, and a thin film transistor having acrystalline silicon film formed on the glass substrate. In addition, adisplay device according to one embodiment of the invention includes asemiconductor device and a display element.

Advantage of the Invention

According to one embodiment of the invention, a glass substrate suitablefor manufacturing a semiconductor device and a display device can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1D show a glass substrate according to an embodiment ofthe invention, which is to be laminated to a silicon substrate; FIG. 1Ais a sectional view before the laminating; FIG. 1B is a sectional viewof a laminated substrate obtained after the laminating; FIG. 1C is asectional view of a semiconductor device; and FIG. 1D is a sectionalview of a display device.

FIG. 2 is a flow chart showing a manufacturing process for manufacturinga semiconductor device and a display device using a glass substrateaccording to the invention.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described below. In the presentdescription, the content of each component in a glass substrate and amethod for manufacturing the same is represented by molar percentagebased on oxides. In addition, in this description, the expression “-”indicating a numerical range is used in the sense to include thenumerical values described before and after the expression as the lowerlimit and the upper limit, as long as not explained otherwise.

FIG. 1A to FIG. 1B are views showing a process for manufacturing asemiconductor device and a display device using a glass substrateaccording to an embodiment of the invention. A glass substrate G1according to the embodiment of the invention shown in FIG. 1A islaminated to a silicon substrate 10, for example, at a temperature of200° C.-700° C. Thus, a laminated substrate 50 shown in FIG. 1B isobtained. A single-crystal silicon substrate is preferred as the siliconsubstrate 10. For example, a full-scale silicon wafer can be used.

The glass substrate GI and the silicon substrate 10 may be laminateddirectly, or may be laminated via a bonding layer 20.

The bonding layer 20 is not limited particularly, as long as it isdurable to the temperature of 200° C.-700° C. For example, the bondinglayer 20 may be formed out of resin, may be formed out of an inorganicinsulating layer, or may be formed out of an organic insulating layer.The bonding layer 20 may include a single layer or may include aplurality of layers.

In addition, when the silicon substrate 10 is a single-crystal siliconsubstrate, a TFT (Thin Film Transistor) having a single-crystal siliconfilm has been formed in a surface of the silicon substrate 10 whichshould be laminated to the glass substrate G1. When the siliconsubstrate 10 is laminated to the glass substrate G1, the thin filmtransistor is transferred onto the glass substrate G1. When the siliconsubstrate 10 is a single-crystal silicon substrate, it can be consideredthat the thin film transistor having the single-crystal silicon film istransferred onto the glass substrate G1. However, through the step oflaminating the silicon substrate 10 on the glass substrate GI or anotherstep, there is a possibility that the single-crystal silicon film of thethin film transistor may be degenerated to cease the existence as thesingle-crystal silicon film. Accordingly, the thin film transistorformed on the glass substrate may include a crystalline silicon filmcategorized in a concept also including polycrystal one.

Next, as shown in FIG. 1C, the silicon substrate 10 of the laminatedsubstrate 50 is formed into a thin film by a predetermined method (forexample, formed into a low profile by mechanical grinding/polishing orchemical etching, or formed into a low profile by a smart cut method).On this occasion, since the thin film transistor has been transferredfrom the glass substrate GI in the step of FIG. 1A and FIG. 1B, asemiconductor device 52 including a TFT (Thin Film Transistor) 30 havingthe single-crystal silicon film formed (transferred) on the glasssubstrate G1 is formed. After that, a predetermined heat treatment and achemical treatment using BHF (Buffered Hydrogen Fluoride) are performed.Finally as shown in FIG. 1D, a display element 40 including a functionalpart for reflecting an image or a video, such as a display cell, islaminated (formed) on the semiconductor device 52. Thus, a displaydevice 54 is formed. A liquid crystal display element or the like can beused as the display element 40. In order to obtain a small-size andultrahigh-definition display, it is preferable to use a self-luminousOLED (Organic Light Emitting Diode) element not requiring a backlight.The display element 40 may be laminated on the glass substrate G1 on theopposite side to the side shown in FIG. 1D.

FIG. 2 is a flow chart showing the manufacturing process. The siliconsubstrate 10 and the glass substrate G1 are laminated to each other(Step S1; corresponding to FIG. 1A). The silicon substrate 10 is formedinto a thin film by a method such as polishing (Step S2; correspondingto FIG. 1C). After that, the semiconductor device 52 is completedthrough the heat treatment (Step S3) and the chemical treatment (StepS4). Then the display element 40 is laminated on the semiconductordevice 52 to complete the display device 54 (Step S5; corresponding toFIG. 1D). Typically to complete the display device, a step such aspatterning is performed between Step S2 and Step S5. Description thereofis omitted for convenience sake.

The following problems have been submitted in the respective steps.

-   Step S1: Warping occurs due to a residual strain caused by a    difference in CTE (Coefficient of Thermal Expansion) between the    glass substrate and the silicon substrate.-   Step S3: A pattern deviates in the thin film transistor due to    thermal shrinkage of the glass substrate (For example, relative to    an original drawing of the pattern designed on the basis of the size    of the glass substrate before the heat treatment, the glass    substrate flowing in the step may be contracted by the heat    treatment. Therefore, when patterning is performed following the    original drawing in a subsequent step, the pattern deviates. The    patterning step in the subsequent step includes an exposure step, a    deposition step, a printing step, etc.).-   Step 4: The glass substrate is clouded.

As for the problem in Step S1, the glass substrate according to oneembodiment of the invention has a small difference in coefficient ofthermal expansion from the silicon substrate. It is therefore possibleto suppress occurrence of a residual strain and warping caused by thedifference in coefficient of thermal expansion in the heat treatmentstep where the glass substrate is laminated to the silicon substrate orin a subsequent heat treatment step.

As for the problem in Step S3, the glass substrate according to oneembodiment of the invention has less compaction, that is, less thermalshrinkage. It is therefore possible to suppress pattern deviation in asubsequent step.

As for the problem in Step S4, the glass substrate according to oneembodiment of the invention is hardly clouded so that lighttransmittance can be secured.

From the aforementioned characteristics, the glass substrate accordingto each embodiment of the invention is suitable as a glass substrate fora miniaturized high-definition display device. Particularly, the glasssubstrate according to each embodiment of the invention can be suitablyused in a display device having an extremely small size such as aneyepiece display (near-eye display), and a semiconductor device fordriving the display device.

In the glass substrate according to one embodiment of the invention, anabsolute value |Δα_(50/100)| of a difference between an averagecoefficient of thermal expansion α_(50/100) of the glass substrate andan average coefficient of thermal expansion of single-crystal silicon at50-100° C., an absolute value |Δα_(100/200)| of a difference between anaverage coefficient of thermal expansion α100/200 of the glass substrateand an average coefficient of thermal expansion of the single-crystalsilicon at 100-200° C., and an absolute value |Δα_(200/300)| of adifference between an average coefficient of thermal expansionα_(200/300) of the glass substrate and an average coefficient of thermalexpansion of the single-crystal silicon at 200-300° C. are 0.16 ppm/° C.or less. The values |Δα_(50/100)|, |Δα_(100/200)| and |Δα_(200/300)| arepreferably 0.15 ppm/° C. or less, more preferably 0.12 ppm/° C. or less,even more preferably 0.10 ppm/° C. or less, and especially preferably0.08 ppm/° C. or less.

When all the three values |Δα_(50/100)|, |Δα_(100/200)| and|Δα_(200/300)| are 0.16 ppm/° C. or less, it is possible to reduce thedifference in coefficient of thermal expansion between the glasssubstrate and the single-crystal silicon, that is, the siliconsubstrate. On the other hand, although the lower limit of each of thethree values is not limited particularly, it may be normally 0.01 ppm/°C. or higher, may be 0.02 ppm/° C. or higher, or may be 0.05 ppm/° C. orhigher.

In the glass substrate according to one embodiment of the invention, theaverage coefficient of thermal expansion α_(50/100) at 50° C.-100° C. ispreferably 2.70 ppm/° C.-3.20 ppm/° C. The average coefficient ofthermal expansion α_(50/100) is preferably 2.80 ppm/° C. or higher, morepreferably 2.90 ppm/° C. or higher, even more preferably 2.91 ppm/° C.or higher, and especially preferably 2.92 ppm/° C. or higher. On theother hand, the average coefficient of thermal expansion α_(50/100) ispreferably 3.10 ppm/° C. or less, more preferably 3.00 ppm/° C. or less,even more preferably 2.96 ppm/° C. or less, and especially preferably2.94 ppm/° C. or less.

When the average coefficient of thermal expansion α_(50/100) is withinthe aforementioned range, the difference in coefficient of thermalexpansion between the glass substrate and the silicon substrate is sosmall that it is possible to secure a process margin while reducing aresidual strain generated in the silicon substrate in the heat treatmentstep where the silicon substrate and the glass substrate are laminatedto each other.

Here, the average coefficient of thermal expansion α_(50/100) at 50°C.-100° C. is an average coefficient of thermal expansion determinedthrough a measurement of coefficient of thermal expansion made over thetemperature range of 50° C.-100° C. by the method as provided for in JISR3102 (year 1995).

In the glass substrate according to one embodiment of the invention, theaverage coefficient of thermal expansion α_(200/300) at 200° C.-300° C.is preferably 3.45 ppm/° C.-3.95 ppm/° C. The average coefficient ofthermal expansion α_(200/300) is preferably 3.55 ppm/° C. or higher,more preferably 3.65 ppm/° C. or higher, even more preferably 3.66 ppm/°C. or higher, and especially preferably 3.68 ppm/° C. or higher. On theother hand, the average coefficient of thermal expansion α_(200/300) ispreferably 3.85 ppm/° C. or less, more preferably 3.75 ppm/° C. or less,even more preferably 3.73 ppm/° C. or less, and especially preferably3.71 ppm/° C. or less.

When the average coefficient of thermal expansion α_(200/300) is withinthe aforementioned range, it is possible to reduce the difference incoefficient of thermal expansion between the glass substrate and thesilicon substrate while securing a process margin when the glasssubstrate is laminated to the silicon substrate. It is thereforepossible to significantly suppress a failure such as a residual straincaused by the difference in coefficient of thermal expansion between theglass substrate and the silicon substrate.

In addition, when the average coefficient of thermal expansion α200/300is within the range of 3.55 ppm/° C.-3.85 ppm/° C., the difference incoefficient of thermal expansion between the glass substrate and thesilicon substrate can be reduced sufficiently. It is therefore possibleto further suppress the failure caused by the difference in coefficientof thermal expansion.

Here, the average coefficient of thermal expansion α_(200/300) at 200°C.-300° C. is an average coefficient of thermal expansion determinedthrough a measurement of coefficient of thermal expansion made over thetemperature range of 200° C.-300° C. by the method as provided for inJIS R3102 (year 1995).

In the glass substrate according to one embodiment of the invention, avalue α_(200/300)/α_(50/100) obtained by dividing the averagecoefficient of thermal expansion α_(200/300) at 200° C.-300° C. by theaverage coefficient of thermal expansion α_(50/100) at 50° C.-100° C. ispreferably 1.10-1.30. When the value α_(200/300)/α_(50/100) is1.10-1.30, the residual strain generated in the silicon substrate in theheat treatment step where the silicon substrate and the glass substrateare laminated to each other can be reduced due to the small differencein coefficient of thermal expansion between the glass substrate and thesilicon substrate. The value α_(200/300)/α_(50/100) is preferably1.18-1.29, more preferably 1.20-1.28, and especially preferably1.24-1.27. The value α200/300/α50/100 may be 1.16 or more and less than1.20.

The glass substrate according to one embodiment of the invention hascompaction of 0.1-100 ppm. The compaction may be 0.5 ppm or higher, maybe 1 ppm or higher, or may be 10 ppm or higher. On the other hand, thecompaction is preferably 80 ppm or less, more preferably 60 ppm or less,even more preferably 50 ppm or less, and especially preferably 40 ppm orless.

The compaction is an index indicating thermal shrinkage under a heattreatment in a temperature range lower than the glass transitiontemperature. When a rate in a slow cooling step which will be describedlater is suppressed, low compaction can be obtained. When the compactionis within the aforementioned range, it is possible to suppress patterndeviation caused by the heat treatment.

The aforementioned compaction is a glass thermal shrinkage generated byrelaxation of a glass structure during a heating treatment. Assume thecompaction in the invention as follows. Two indentations are made at apredetermined interval in a surface of the glass substrate. After that,the glass substrate is heated from a room temperature to 600° C. at arate of 100° C./hour, kept at 600° C. for 80 minutes, and then cooleddown to the room temperature at a rate of 100° C./hour. The compactionin the invention means a shrinkage (ppm) of the interval between theindentations in this case.

The compaction in the invention can be measured by the following method.The surface of the glass substrate is polished to obtain a samplemeasuring 100 mm×20 mm. Dot-like indentations are made at two places andat an interval A (A=95 mm) in the longitudinal direction of the surfaceof the sample.

Next the sample is heated from the room temperature to 600° C. at thetemperature rising rate of 100° C./hour(=1.6° C./minute), and kept at600° C. for 80 minutes. The sample is then cooled down to the roomtemperature at the temperature falling rate of 100° C./hour. Theinterval between the indentations is measured again. The measuredinterval is set as B. From the intervals A and B obtained thus, thecompaction is calculated using the following expression. The intervals Aand B are measured by use of an optical microscope.

compaction [ppm]=(A−B)/A×10⁶

In the glass substrate according to one embodiment of the invention, ahaze at the time of BHF treatment (hereinafter also referred to as BHFhaze) is preferably 40% or less. The haze is preferably 35% or less,more preferably 30% or less, even more preferably 25% or less, andespecially preferably 20% or less.

The haze is an index about transparency of the glass substrate. When thehaze is within the aforementioned range, the glass substrate issuppressed from being clouded in the chemical treatment, so that lighttransmittance can be secured.

The BHF haze in the invention is a ratio of light scattered bycloudiness of glass as follows. The glass is immersed in a solution inwhich 50 mass % hydrofluoric acid and 40 mass % ammonium fluorideaqueous solution have been mixed at 1:9 (volume ratio), at 25° C. for 20minutes, then washed and dried. After that, the glass is exposed tolight. The BHF haze is a ratio of the light scattered by cloudiness ofthe glass on this occasion. The haze value is measured by a haze metermanufactured by Suga Test Instruments Co., Ltd.

The glass substrate according to one embodiment of the invention is aso-called alkali-free glass substrate in which the content of alkalimetal oxides has been suppressed. The content of alkali metal oxides ispreferably 0%-0.1%. Here, the alkali metal oxides include Li₂O, Na₂O,and K₂O. When the content of alkali metal oxides is 0.1% or less, alkaliions are hardly dispersed in the silicon substrate in the heat treatmentstep where the silicon substrate and the glass substrate are laminatedto each other. The content of alkali metal oxides is more preferably0.05% or less, even more preferably 0.03% or less, and especiallypreferably substantially nil. Here, the phrase “the content of alkalimetal oxides is substantially nil” means that no alkali metal oxide iscontained, or alkali metal oxides may be contained as impurities whichhave unavoidably come into the glass substrate during the production.

Preferably the glass substrate according to one embodiment of theinvention has the following composition.

SiO₂: 50%-75%

Al₂O₃: 6%-16%

B₂O₃: 0%-15%

MgO: 0%-15%

CaO: 0%-13%

SrO: 0%-11%

BaO: 0%-9.5%

SiO₂ is a component which forms a network of glass. When the content ofSiO₂ is 50% or higher, the glass has improved heat resistance, chemicalresistance and weatherability. When the content of SiO₂ is 75% or less,the glass can be prevented from having too high melt viscosity and canhave satisfactory meltability. The content of SiO₂ is preferably 60% orhigher, and more preferably 65% or higher. On the other hand, thecontent of SiO₂ is preferably 70% or less, more preferably 68% or less,and especially preferably 67% or less.

When the content of Al₂O₃ is 6% or higher, the glass has improvedweatherability, heat resistance and chemical resistance, and has ahigher Young's modulus. In addition, the glass has a higher straintemperature. Thus, the compaction value can be reduced. When the contentof Al₂O₃ is 16% or less, the glass can be prevented from having too highmelt viscosity and can have satisfactory meltability. Thus, the glass ishardly devitrified. The content of Al₂O₃ is preferably 8% or higher,more preferably 11% or higher, and especially preferably 12% or higher.On the other hand, the content of Al₂O₃ is preferably 14% or less, andmore preferably 13.5% or less.

B₂O₃ is not an essential component. However, when B₂O₃ is contained, theglass can be prevented from having too high melt viscosity and can havesatisfactory meltability. Thus, the glass is hardly devitrified. Whenthe content of B₂O₃ is 15% or less, the glass transition temperature canbe increased to increase its Young's modulus. The content of B₂O₃ ispreferably 3% or higher, and especially preferably 4% or higher. Inorder to suppress the compaction value from being too high, the contentof B₂O₃ is preferably 12% or less, more preferably 10% or less, andespecially preferably 6% or less.

MgO is not an essential component. However, when MgO is contained, theglass can be prevented from having too high melt viscosity and can havesatisfactory meltability, improved weatherability, and enhanced Young'smodulus. When the content of MgO is 15% or less, the glass is hardlydevitrified. The content of MgO is preferably 4% or higher, and morepreferably 6% or higher. On the other hand, the content of MgO ispreferably 10% or less, more preferably 9.5% or less, and even morepreferably 9% or less.

CaO is not an essential component. However, when CaO is contained, theglass can be prevented from having too high melt viscosity and can havesatisfactory meltability, and improved weatherability. When the contentof CaO is 13% or less, the glass is hardly devitrified. The content ofCaO is preferably 1% or higher, more preferably 2% or higher, andespecially preferably 4% or higher. On the other hand, the content ofCaO is preferably 10% or less, more preferably 8% or less, andespecially preferably 7% or less.

SrO is not an essential component. However, when SrO is contained, theglass can be prevented from having too high melt viscosity and can havesatisfactory meltability, and improved weatherability. When the contentof SrO is 11% or less, the glass is hardly devitrified. The content ofSrO is preferably 0.5% or higher, and more preferably 1% or higher. Onthe other hand, the content of SrO is preferably 8% or less, morepreferably 6% or less, and even more preferably 3% or less.

BaO is not an essential component. However, when BaO is contained, theglass can be prevented from having too high melt viscosity and can havesatisfactory meltability, and improved weatherability. When the contentof BaO is 9.5% or less, the glass is hardly devitrified. The content ofBaO is preferably 3% or less, more preferably 2% or less, and especiallypreferably 0.5% or less.

In the glass substrate according to one embodiment of the invention, thetotal content of CaO, SrO, and BaO is preferably 5% or higher. When thetotal content of CaO, SrO, and BaO is 5% or higher, the glass is hardlydevitrified. The total content of CaO, SrO, and BaO is preferably 6% orhigher, more preferably 7% or higher, and even more preferably 7.5% orhigher. On the other hand, the total content of CaO, SrO, and BaO may be15% or less, may be 10% or less, or may be 9% or less.

In the glass substrate according to one embodiment of the invention, itis preferable that a relation of (content of Al₂O₃)≥content of MgO) issatisfied. When the relation of (content of Al₂O₃)≥(content of MgO) issatisfied, the average coefficient of thermal expansion of the glasssubstrate can be easily matched with the average coefficient of thermalexpansion of the silicon substrate. Thus, it is possible to reduce theresidual strain generated in the silicon substrate in the heat treatmentstep where the silicon substrate and the glass substrate are laminatedto each other.

The glass substrate according to one embodiment of the inventionpreferably has a devitrification viscosity (η_(TL)) of 103.8 dPa·s orhigher. When the devitrification viscosity is 10^(3.8) d·Pa·s or higher,the glass substrate can be formed stably. The devitrification viscosityis more preferably 10^(3.9) d·Pa·s or higher, and even more preferably10^(4.02) dPa·s or higher.

In the glass substrate according to one embodiment of the invention, thecontent of Fe₂O₃ is preferably 0.01% or less in order to make itdifficult for the glass substrate to absorb visible light when the glasssubstrate is, for example, used as a substrate of a device fordisplaying an image or a video. The content of Fe₂O₃ is more preferably0.006% or less, and even more preferably 0.004% or less.

Preferably the glass substrate according one embodiment of the inventionhas a content of Fe₂O₃ higher than 0.001% and 0.04% or less in order toenhance its thermal conductivity and improve its meltability. When thecontent of Fe₂O₃ is higher than 0.001%, it is possible to enhance thethermal conductivity of the glass substrate and improve the meltabilitythereof. When the content of Fe₂O₃ is 0.04% or less, the glass substratecan be prevented from absorbing visible light too powerfully.

The content of Fe₂O₃ is preferably 0.0015% or higher, and morepreferably 0.002% or higher. The content of Fe₂O₃ is more preferably0.035% or less, even more preferably 0.03% or less, and especiallypreferably 0.025% or less.

The glass substrate according to one embodiment of the invention maycontain a refining agent such as SnO₂, SO₃, Cl, and F.

The glass substrate according to one embodiment of the invention maycontain, for example, ZnO, Li₂O, WO₃, Nb₂O₅, V₂O₅, Bi₂O₃, MoO₃, P₂O₅,Ga₂O₃, I₂O₅, In₂O₅, Ge₂O₅, etc in order to improve weatherability,meltability, devitrification, ultraviolet ray shielding, infrared rayshielding, ultraviolet ray transmittance, infrared ray transmittance,etc.

The glass substrate according to one embodiment of the invention maycontain ZrO₂, Y₂O₃, La₂O₃, TiO₂, and SnO₂ by a total amount of 2% orless, in order to improve the chemical resistance of the glass. Thetotal content of ZrO₂, Y₂O₃, La₂O₃, TiO₂, and SnO₂ is preferably 1% orless, and more preferably 0.5% or less. Of these, Y₂O₃, La₂O₃, and TiO₂also contributes to improvement in the Young's modulus of the glass.

The glass substrate according to one embodiment of the inventionpreferably contains substantially neither As₂O₃ nor Sb₂O₃ from thestandpoint of environmental burden. The glass substrate preferablycontains substantially no ZnO from the standpoint of stable formabilityin a float process.

In the glass substrate according to one embodiment of the invention, theaverage coefficient of thermal expansion α_(100/200) at 100° C.-200° C.is preferably 3.13 ppm/° C.-3.63 ppm/° C., and more preferably 3.23ppm/° C.-3.53 ppm/° C. When the average coefficient of thermal expansionα_(100/200) is within the aforementioned range, the difference incoefficient of thermal expansion between the glass substrate and thesilicon substrate is so small that it is possible to secure a processmargin while reducing the residual strain generated in the siliconsubstrate in the heat treatment step where the silicon substrate and theglass substrate are laminated to each other.

α_(100/200) is preferably 3.33 ppm/° C. or higher, more preferably 3.34ppm/° C. or higher, and especially preferably 3.35 ppm/° C. or higher.On the other hand, α_(100/200) is preferably 3.44 ppm/° C. or less, morepreferably 3.43 ppm/° C. or less, even more preferably 3.41 ppm/° C. orless, and especially preferably 3.38 ppm/° C. or less.

Here, the average coefficient of thermal expansion α_(100/200) at 100°C.-200° C. is an average coefficient of thermal expansion determinedthrough a measurement of coefficient of thermal expansion made over thetemperature range of 100° C.-200° C. by the method as provided for inJIS R3102 (year 1995).

The glass substrate according to one embodiment of the invention has aYoung's modulus of 60 GPa or more. When the Young's modulus is 60 GPa ormore, the glass substrate can be suppressed from warping or cracking ina slow cooling step when the glass substrate is manufactured. Inaddition, it is possible to suppress damage of the glass substratecaused by contact with the silicon substrate, a peripheral member, etc.The Young's modulus is more preferably 65 GPa or more, even morepreferably 70 GPa or more, and especially preferably 80 GPa or more.

On the other hand, the Young's modulus is preferably 100 GPa or less.When the Young's modulus is preferably 100 GPa or less, the glass can besuppressed from being brittle, and the glass substrate can be inhibitedfrom chipping during cutting or dicing. The Young's modulus thereof ismore preferably 90 GPa or less, and even more preferably 87 GPa or less.

The glass substrate according to one embodiment of the inventionpreferably has a thickness of 1.0 mm or less. When the thickness is 1.0mm or less, a display device can be formed to be low in profile. Thethickness is more preferably 0.8 mm or less, even more preferably 0.7 mmor less, and especially preferably 0.5 mm or less.

On the other hand, the thickness of the glass substrate is preferably0.05 mm or more. When the thickness is 0.05 mm or more, the glasssubstrate can be inhibited from being damaged by contact with thesilicon substrate, a peripheral member, etc. In addition, the glasssubstrate can be inhibited from being bent by its own weight. Thethickness is more preferably 0.1 mm or more, and even more preferably0.3 mm or more.

Preferably in the glass substrate according to one embodiment of theinvention, one main surface thereof has an area of 0.03 m² or larger.When the area is 0.03 m² or larger, the silicon substrate having a largearea can be used so that a large number of display devices can bemanufactured from one laminated substrate. The area is more preferably0.04 m² or larger, and even more preferably 0.05 m² or larger.

In addition, in the glass substrate according to one embodiment of theinvention, the values |Δα_(50/100)|, |Δα_(100/200)| and |Δα_(200/300)|are 0.16 ppm/° C. or less. Accordingly, even when the area reaches 0.03m² or larger, the residual strain generated in the silicon substrate canbe reduced in the heat treatment step where the silicon substrate andthe glass substrate are laminated to each other. The area is preferably0.1 m² or less. When the area is preferably 0.1 m² or less, it is easyto handle the glass substrate, so that the glass substrate can beinhibited from being damaged by contact with the silicon substrate, aperipheral member, etc. The area is more preferably 0.08 m² or less, andeven more preferably 0.06 m² or less.

The glass substrate according to one embodiment of the inventionpreferably has a density of 2.60 g/cm³ or less. When the density is 2.60g/cm³ or less, the glass substrate is light in weight. In addition, theglass substrate can be suppressed from being bent by its own weight. Thedensity is more preferably 2.55 g/cm³ or less, even more preferably 2.50g/cm³ or less, and especially preferably 2.48 g/cm³.

On the other hand, the density is preferably 2.20 g/cm³ or higher. Whenthe density is 2.20 g/cm³ or higher, the glass can have a heightenedVickers hardness. Thus, it is possible to make it difficult to scratchthe glass surface. The density is more preferably 2.30 g/cm³ or higher,even more preferably 2.40 g/cm³ or higher, and especially preferably2.45 g/cm³ or higher.

In the glass substrate according to one embodiment of the invention, adensity of defects included in the glass substrate is preferably 1defect/cm² or less. The defects included in the glass substrate includebubbles, flaws, metal foreign substances such as platinum, unmelted rawmaterials, etc. existing in the surface or the inside of the glasssubstrate, each having a size of 1 mm or smaller and 0.5 μm or larger. Adefect larger than 1 mm can be visually determined easily, and asubstrate having such a defect can be removed easily. A defect smallerthan 0.5 μm is so small that there is less possibility that the defectmay affect the characteristics of an element even when the substrate isused as a substrate of an ultrahigh-definition display. In a liquidcrystal display device, particularly in a bottom-emission OLED displaydevice, visual recognition is performed from the glass substrate side.Accordingly, high-quality management of defects is required. The densityof defects is more preferably 0.1 defect/cm² or less, and even morepreferably 0.01 defect/cm² or less.

The glass substrate according to one embodiment of the invention is notparticularly limited as to the shape thereof. The glass substrate may becircular, elliptical or rectangular, and may have a notch or orientationflat formed in the edge thereof in order to be matched with the shape ofthe silicon substrate to be laminated thereto. When the glass substrateis circular, some of the periphery of the glass substrate may bestraight.

The glass substrate according to one embodiment of the inventionpreferably has a strain temperature of 650° C. or higher. When thestrain temperature is 650° C. or higher, a dimensional change of theglass substrate during the heat treatment step can be suppressed. Thestrain temperature is preferably 700° C. or higher, more preferably 720°C. or higher, and even more preferably 740° C. or higher.

A manufacturing method for improving a low thermal shrinkage propertymay be applied to the alkali-free glass in one embodiment of theinvention. Specifically, it is preferable that an equivalent coolingrate q_(eq) is made not higher than 400° C./min. Here, the equivalentcooling rate is defined and evaluated in the following manner.

A glass processed into a cube measuring 10 mm×10 mm×0.3 mm-2.0 mm iskept at a temperature higher than its strain temperature by 170° C. for5 minutes by use of an infrared heating type electric furnace. Afterthat, the glass is cooled down to a room temperature (25° C.). On thisoccasion, a plurality of glass samples distributed within a range of thecooling rate from 1° C./min to 1,000° C./min are made up.

A refractive index n_(d) of a d-line (wavelength 587.6 nm) in each ofthe glass samples is measured by a V-block method using KPR-2000manufactured by Shimadzu Corporation.

Each refractive index n_(d) obtained thus is plotted on the logarithm ofthe cooling rate corresponding thereto. Thus, a calibration curve ofn_(d) on the cooling rate is obtained.

Next, n_(d) of a glass actually manufactured through steps of melting,forming, cooling, etc. is measured in the aforementioned measurementmethod. A cooling rate corresponding to the obtained n_(d) (referred toas equivalent cooling rate in this embodiment) is obtained from theaforementioned calibration curve.

The equivalent cooling rate is preferably 400° C./min or less, morepreferably 350° C./min or less, and even more preferably 100° C./min orless. On the other hand, when the equivalent cooling rate is too low,the productivity of the glass substrate deteriorates. Therefore, theequivalent cooling rate is preferably 0.1° C./min or higher, morepreferably 1° C./min or higher, and even more preferably 10° C./min orhigher.

In the glass substrate according to one embodiment of the invention, atemperature at which the viscosity of the glass substrate reaches 102dPa·s (also referred to as T₂) is preferably 1,800° C. or less. T₂ ismore preferably 1,750° C. or less, even more preferably 1,700° C. orless, and especially preferably 1,650° C. or less.

In the glass substrate according to one embodiment of the invention, atemperature at which the viscosity of the glass substrate reaches 10⁴dPa·s (also referred to as T₄) is preferably 1,350° C. or less. T₄ ismore preferably 1,300° C. or less, even more preferably 1,295° C. orless, and especially preferably 1,290° C. or less. In consideration ofeasiness to secure other properties, T₄ is 1,100° C. or higher.

In the glass substrate according to one embodiment of the invention, adevitrification temperature thereof is preferably 1,325° C. or less,more preferably 1,320° C. or less, even more preferably 1,310° C. orless, and especially preferably 1,295° C. or less. A devitrificationtemperature of a glass is obtained as follows. Crushed particles of theglass are placed on a platinum dish and heat-treated for 17 hours in anelectric furnace controlled so as to have a constant temperature. Theheat-treated glass is examined with an optical microscope to determine ahighest temperature at which crystal precipitation occurs inside theglass and a lowest temperature at which crystal precipitation does notoccur inside the glass. The devitrification temperature of the glass isan average value of the highest temperature and the lowest temperature.

The glass substrate according to one embodiment of the inventionpreferably satisfies:

0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ q_(eq)) is 2.70-3.20;

0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913×(content of MgO)+0.1621×(content of CaO)+0.1900×(content ofSrO)+0.2180×(content of BaO)+0.0391×(log₁₀ q_(eq)) is 3.13-3.63;

0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ q_(eq)) is 3.45-3.95; and

0.0111×(content of SiO₂)+0.0250×(content of Al₂O₃)+0.0078×(content ofB₂O₃)+0.0144×(content of MgO)+0.0053×(content of CaO)+0.0052×(content ofSrO)+0.0013×(content of BaO)−0.0041×(log_(i0) q_(eq)) is 1.10-1.30.

Here, the content of SiO₂, the content of Al₂O₃, the content of B₂O₃,the content of MgO, the content of CaO, the content of SrO, and thecontent of BaO are contents of respective components contained in theobtained glass, and q_(eq) is an equivalent cooling rate.

When the glass substrate satisfies those conditions, it is possible tosecure a process margin while easily reducing a residual straingenerated in the silicon strain in the heat treatment step where thesilicon substrate and the glass substrate are laminated to each other.

0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ q_(eq)) is preferably 2.80 ormore, more preferably 2.90 or more, even more preferably 2.91 or more,and especially preferably 2.92 or more.

On the other hand, 0.0177×(content of SiO₂)−0.0173×(content ofAl₂O₃)+0.0377×(content of B₂O₃)+0.0771×(content of MgO)+0.1543×(contentof CaO)+0.1808×(content of SrO)+0.2082×(content of BaO)+0.0344×(log₁₀q_(eq)) is preferably 3.10 or less, more preferably 3.00 or less, evenmore preferably 2.96 or less, and especially preferably 2.94 or less.

0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913×(content of MgO)+0.1621×(content of CaO)+0.1900×(content ofSrO)+0.2180×(content of BaO)+0.0391×(log₁₀ q_(eq)) is preferably 3.23 ormore, more preferably 3.33 or more, even more preferably 3.34 or more,and especially preferably 3.35 or more.

On the other hand, 0.0181×(content of SiO₂)+0.0004×(content ofAl₂O₃)+0.0387×(content of B₂O₃)+0.0913×(content of MgO)+0.1621×(contentof CaO)+0.1900×(content of SrO)+0.2180×(content of BaO)+0.0391'(log₁₀q_(eq)) is preferably 3.53 or less, more preferably 3.43 or less, evenmore preferably 3.41 or less, and especially preferably 3.38 or less.

0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ q_(eq)) is preferably 3.55 ormore, more preferably 3.65 or more, even more preferably 3.66 or more,and especially preferably 3.68 or more.

On the other hand, 0.0177×(content of SiO₂)+0.0195×(content ofAl₂O₃)+0.0323×(content of B₂O₃)+0.1015×(content of MgO)+0.1686×(contentof CaO)+0.1990×(content of SrO)+0.2179×(content of BaO)+0.0312×(log₁₀q_(eq)) is preferably 3.85 or less, more preferably 3.73 or less, evenmore preferably 3.65 or less, and especially preferably 3.71 or less.

Further, 0.0111×(content of SiO₂)+0.0250×(content ofAl₂O₃)+0.0078×(content of B₂O₃)+0.0144×(content of MgO)+0.0053×(contentof CaO)+0.0052×(content of SrO)+0.0013×(content of BaO)−0.0041×(log₁₀q_(eq)) is preferably 1.20 or more.

On the other hand, 0.0111×(content of SiO₂)+0.0250×(content ofAl₂O₃)+0.0078×(content of B₂O₃)+0.0144×(content of MgO)+0.0053×(contentof CaO)+0.0052×(content of SrO)+0.0013×(content of BaO)−0.0041×(log₁₀q_(eq)) is preferably 1.27 or less.

In the glass substrate according to one embodiment of the invention,when the glass substrate has a thickness of 0.5 mm, a transmittance oflight at a wavelength of 300 nm is preferably 55% or higher, morepreferably 60% or higher, even more preferably 70% or higher, andespecially preferably 75% or higher. When the transmittance at thewavelength of 300 nm is high, a bonding layer can be separatedefficiently by irradiation with ultraviolet rays through the glasssurface, or an oriented film can be aligned efficiently when the glasssubstrate is applied to a liquid crystal display.

In the glass substrate according to one embodiment of the invention, aweight reduction amount in a hydrofluoric acid aqueous solution (HF)(hereinafter also referred to as HF weight reduction amount) ispreferably 0.05 (mg/cm²)/min or higher and 0.20 (mg/cm²)/min or less.Here, the HF weight reduction amount is a reduction amount((mg/cm²)/min) per unit area and unit time when the glass substrate isimmersed in a 5 mass % hydrofluoric acid aqueous solution at 25° C.

The glass substrate according to one embodiment of the invention may beinstalled directly as a part of a device after the glass substrate islaminated to the silicone substrate. For example, the glass substrate isinstalled as a display substrate in the device. In such a case, it ispreferable to slim the glass substrate in order to miniaturize thedevice. Therefore, in the glass substrate according to one embodiment ofthe invention, it is more preferable that the slimming rate is higher.The HF weight reduction amount may be used as an index of the slimmingrate of the glass substrate.

When the HF weight reduction amount is 0.05 (mg/cm²)/min or higher, theproductivity in the slimming step can be improved and thus it ispreferable. On the other hand, when the HF weight reduction amount is0.20 (mg/cm²)/min or less, it is possible to prevent such a failure thatsmoothness may be lost in the surface of the glass substrate due tounevenness in etching depth and thus it is preferable.

The HF weight reduction amount is more preferably 0.07 (mg/cm²)/min orhigher, even more preferably 0.09 (mg/cm²)/min or higher, and especiallypreferably 0.11 (mg/cm²)/min or higher. On the other hand, the HF weightreduction amount is more preferably 0.18 (mg/cm²)/min or less, even morepreferably 0.16 (mg/cm²)/min or less, and especially preferably 0.14(mg/cm²)/min or less.

In the glass substrate according to one embodiment of the invention, aphotoelastic constant thereof is preferably 33 nm/(MPa·cm) or less, morepreferably 32 nm/(MPa·cm) or less, even more preferably 31 nm/(MPa·cm)or less, especially preferably 30 nm/(MPa·cm) or less, and mostpreferably 29 nm/(MPa·cm) or less. When the photoelastic constant is 33nm/(MPa·cm) or less, poor image quality can be prevented from occurringeasily in the display device.

The laminated substrate according to one embodiment of the invention isformed by a lamination of the aforementioned glass substrate and asilicon substrate. Due to a small difference in coefficient of thermalexpansion between the silicon substrate and the glass substrate, aresidual strain generated in the silicon substrate can be reduced in theheat treatment step where the silicon substrate and the glass substrateare laminated to each other. The laminated substrate may be obtained bylaminating the glass substrate and the silicon substrate to each othervia a resin interposed therebetween.

On this occasion, warping of the laminated substrate as a whole may beaffected by the thickness of the resin, the coefficient of thermalexpansion of the resin, the heat treatment temperature during thelaminating, etc. The laminated substrate according to one embodiment ofthe invention, the coefficient of thermal expansion can be controlled asin the glass substrate according to one of the aforementionedembodiments of the invention, so that the warping of the laminatedsubstrate as a whole can be reduced. Thus, it is possible to expand aprocess margin for the thickness of the resin, the coefficient ofthermal expansion of the resin, the heat treatment temperature duringthe laminating, etc. The glass substrate according to one of theaforementioned embodiments of the invention can be applied to thelaminated substrate according to one embodiment of the invention.

Next, a method for manufacturing a glass substrate according to oneembodiment of the invention will be described.

A glass substrate according to one embodiment of the invention ismanufactured though a melting step of heating raw glass materials toobtain molten glass, a refining step of removing bubbles from the moltenglass, a forming step of forming the molten glass into a plate-likeshape to obtain a glass ribbon, and an slow cooling step of graduallycooling the glass ribbon down to a room temperature state.

In the melting step, raw materials are prepared to have a composition ofa glass plate which should be obtained. The raw materials arecontinuously thrown into a melting furnace, and preferably heated toabout 1,450° C.-1,650° C. to obtain molten glass.

Oxides, carbonates, nitrates, hydroxides, halides such as chlorides,etc. can be used as the raw materials. When the melting or refining stepincludes a step in which the molten glass comes into contact withplatinum, fine platinum particles may come into the molten glass and beincluded as foreign matter in the glass plate obtained. Nitrates used asraw materials has an effect of preventing the platinum from coming intothe molten glass as foreign matter.

Strontium nitrate, barium nitrate, magnesium nitrate, calcium nitrate,etc. can be used as the nitrates. It is more preferred to use strontiumnitrate. With respect to the particle sizes of the raw materials,various raw materials can be suitably used, ranging from raw materialshaving a particle diameter of several hundred micrometers that is largeenough not to remain unmelted to raw materials having a particlediameter of several micrometers that is small enough neither to fly offduring raw-material conveyance nor to aggregate into secondaryparticles. Granules can be also used. The water contents of the rawmaterials can be suitably regulated in order to prevent the rawmaterials from flying off. Melting conditions including 13-OH and thedegree of oxidation/reduction of Fe or Redox [Fe²⁺/(Fe²⁺+Fe³⁺)] can bealso suitably regulated.

Next, the refining step is a step of removing bubbles from the moltenglass obtained in the aforementioned melting step. As the refining step,a method of degassing under reduced pressure may be applied. Forproducing the glass substrate according to the invention, SO₃ or SnO₂can be used as a refining agent. Preferred SO₃ sources are the sulfatesof at least one element selected from among Al, Mg, Ca, Sr, and Ba. Morepreferred are the sulfates of alkaline earth metals. Of those,CaSO₄.2H₂O, SrSO₄, and BaSO₄ are especially preferred because of theirconspicuous effect of enlarging bubbles.

As a refining agent for the method of degassing performed under reducedpressure, it is preferred to use a halogen such as Cl or F. Preferred Clsources are the chlorides of at least one element selected from amongAl, Mg, Ca, Sr, and Ba. More preferred are the chlorides of alkalineearth metals. Of those, SrCl₂.6H₂O and BaCl₂.2H₂O are especiallypreferred because of their conspicuous effect of enlarging bubbles andtheir low deliquescence. Preferred F sources are the fluorides of atleast one element selected from among Al, Mg, Ca, Sr, and Ba. Morepreferred are the fluorides of alkaline earth metals. Of those, CaF₂ ispreferred because of its conspicuous effect of enhancing the meltabilityof raw glass materials.

Next, the forming step is a step where the molten glass from whichbubbles have been removed in the aforementioned refining step is formedinto a plate-like shape to obtain a glass ribbon. A float process isapplied to the forming step. In the float process, the molten glass ispoured onto a molten metal to obtain a plate-shaped glass ribbon.

Next, the annealing step is a step where the glass ribbon obtained inthe aforementioned forming step is gradually cooled down to a roomtemperature state. As the annealing step, the glass ribbon is graduallycooled down to the room temperature state so that an average coolingrate from a temperature at which the viscosity is 10¹³ dPa·s to atemperature at which the viscosity reaches 10^(1.45) dPa·s is R. Theannealed glass ribbon is cut to obtain the glass substrate.

In the method for manufacturing the glass substrate according to oneembodiment of the invention, the obtained glass substrate has thefollowing composition, as represented by molar percentage based onoxides.

SiO₂: 50%-75%

Al₂O₃: 6%-16%

B2O₃: 0%-15%

MgO: 0%-15%

CaO: 0%-13%

SrO: 0%-11%

BaO: 0%-9.5%

In the method for manufacturing the glass substrate according to oneembodiment of the invention, the composition of the obtained glasssubstrate and the average cooling rate R (° C./min) in the annealingstep from the temperature at which the viscosity of the glass ribbon is10¹³ dPa·s to the temperature at which the viscosity reaches 10^(14.5)dPa·s satisfy the following conditions (1) to (4).

0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ R) is 2.70-3.20;   Condition(1):

0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913×(content of MgO)+0.1621×(content of CaO)+0.1900×(content ofSrO)+0.2180×(content of BaO)+0.0391×(log₁₀ R) is 3.13-3.63;   Condition(2):

0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ R) is 3.45-3.95; and  Condition (3):

0.0111×(content of SiO₂)+0.0250×(content of Al₂O₃)+0.0078×(content ofB₂O₃)+0.0144×(content of MgO)+0.0053×(content of CaO)+0.0052×(content ofSrO)+0.0013 ×(content of BaO)−0.0041×(log₁₀ R) is 1.10-1.30.   Condition(4):

Preferably the following conditions (1) to (4) are satisfied.

0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ R) is 2.70-3.20;   Condition(1):

0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913×(content of MgO)+0.1621×(content of CaO)+0.1900×(content ofSrO)+0.2180×(content of BaO)+0.0391×(log₁₀ R) is 3.13-3.63;   Condition(2):

0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ R) is 3.45-3.95; and  Condition (3):

0.0111×(content of SiO₂)+0.0250×(content of Al₂O₃)+0.0078×(content ofB₂O₃)+0.0144×(content of MgO)+0.0053×(content of CaO)+0.0052×(content ofSrO)+0.0013 ×(content of BaO)−0.0041×(log₁₀ R) is 1.10-1.30.   Condition(4):

Here, the content of SiO₂, the content of Al₂O₃, the content of B₂O₃,the content of MgO, the content of CaO, the content of SrO, and thecontent of BaO are contents of respective components contained in theobtained glass. When the glass substrate satisfies the conditions (1) to(4), it is possible to manufacture the glass substrate in which theresidual strain generated in the silicon strain in the heat treatmentstep can be reduced.

The invention is not limited to the aforementioned embodiments.Modifications, improvements, etc. within the scope where the object ofthe invention can be attained are included in the invention.

For example, when the glass substrate according to one embodiment of theinvention is manufactured, a fusion process, a press forming process, orthe like, may be applied to the forming step to form molten glass into aplate-like shape.

In addition, when the glass substrate according to one embodiment of theinvention is manufactured, a platinum crucible may be used. When theplatinum crucible is used, the melting step is arranged as follows. Thatis, raw materials are prepared to have a composition of the glasssubstrate which should be obtained. The platinum crucible in which theraw materials have been put is thrown into an electric furnace, andpreferably heated to about 1,450° C.-1,650° C. A platinum stirrer isinserted into the platinum crucible to stir the raw materials for 1 hourto 3 hours. Thus, molten glass is obtained.

In the forming step, the molten glass is, for example, poured onto acarbon plate, and formed into a plate-like shape. In the annealing step,the plate-like glass is gradually cooled down to a room temperaturestate, and cut to obtain a glass substrate.

In addition, the glass substrate obtained by cutting may be, forexample, heated to about Tg+50° C., and then gradually cooled down tothe room temperature state. In this manner, the equivalent cooling rateq_(eq) can be adjusted.

The invention will be described specifically along its examples.However, the invention is not limited to the examples.

Various raw glass materials including silica sand were prepared so as toresult in each of the glass compositions (target compositions) shown inTable 1. The raw materials were put into a platinum crucible, and heatedat a temperature of 1,550° C.-1,650° C. for 3 hours in an electricfurnace so as to be melted. Thus, molten glass was obtained. During themelting, a platinum stirrer was inserted into the platinum crucible tostir the raw materials for 1 hour to thereby homogenize the glass. Themolten glass was poured onto a carbon plate, and formed into aplate-like shape. After that, the plate-like glass was put into theelectric furnace at a temperature of about Tg+50° C. so that thetemperature of the glass was decreased in the electric furnace at acooling rate R (° C./min). Thus, the glass was cooled to reach the roomtemperature.

The obtained glass was evaluated as to values obtained from thefollowing expressions (1) to (4), average coefficient of thermalexpansion (ppm/° C.), compaction (ppm), BUY haze (%), Young's modulus(GPa), density (g/cm³), strain temperature (° C.), transmittance (%), T₂(° C.), T₄ (° C.), devitrification temperature (° C.), devitrificationviscosity log₁₀ η_(TL) (dPa sec), and photoelastic constant[nm/(MPa·cm)]. Results obtained about seven examples are shown inTable 1. Table 1 also shows α_(200/300)/α_(50/100), |Δα_(50/100)|,|Δα_(100/200)|, |Δα_(200/300)|, and average cooling rate (° C./min).

0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ R) is 2.70-3.20;   Expression(1):

0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913×(content of MgO)+0.1621×(content of CaO)+0.1900×(content ofSrO)+0.2180×(content of BaO)+0.0391×(log₁₀ R) is 3.13-3.63;   Expression(2):

0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ R) is 3.45-3.95; and  Expression (3):

0.0111×(content of SiO₂)+0.0250×(content of Al₂O₃)+0.0078×(content ofB₂O₃)+0.0144×(content of MgO)+0.0053×(content of CaO)+0.0052×(content ofSrO)+0.0013 ×(content of BaO)−0.0041×(log₁₀ R) is 1.10-1.30.  Expression (4):

Values in parentheses in the table are calculated values.

Methods for measuring the respective physical properties will be shownbelow.

(Average Coefficient of Thermal Expansion)

The average coefficient of thermal expansion was measured by adifferential dilatometer (TMA) in accordance with the method as providedfor in JIS R3102 (year 1995). α_(50/100) was measured in a temperaturerange of 50° C.-100° C. α_(100/200) was measured in a temperature rangeof 100° C.-200° C. α_(200/300) was measured in a temperature range of200° C.-300° C.

(Average Coefficient of Thermal Expansion of Silicon Substrate)

Table 2 shows an average coefficient of thermal expansion of a siliconsubstrate (manufactured by Shin-Etsu Chemical Co., Ltd.) made ofsingle-crystal silicon. α_(Si50/100) of the silicon substrate was 2.94ppm/° C. α_(Si100/200) of the silicon substrate was 3.37 ppm/° C.α_(si200/300) of the silicon substrate was 3.69 ppm/° C.α_(Si200/300)/α_(Si50/100) was 1.25. Typically the average coefficientof thermal expansion of the silicon substrate is a value shown in Table2.

(Compaction)

The compaction was calculated based on measurement of an intervalbetween indentations of each sample as described previously.

(BHF Haze)

As described previously, each sample was immersed in a solution in which50% hydrofluoric acid and 40% ammonium fluoride aqueous solution hadbeen mixed. After that, the BHF haze of the sample was measured by ahaze meter manufactured by Suga Test Instruments Co., Ltd.

(HF Weight Reduction Ratio)

As described previously, a glass mirror-finished to be 40 mm square wasimmersed into a 5 mass % hydrofluoric acid aqueous solution at 25° C.for 20 minutes. A weight reduction amount was obtained from weights ofthe glass measured before and after the immersion. The weight reductionamount for 20 minutes was converted into an amount per one minute. Thus,a reduction amount per unit area and unit time ((mg/cm²/min) wasobtained.

(Young's Modulus)

A glass having a thickness of 0.5 mm-10 mm was measured for Young'smodulus by an ultrasonic pulse method.

(Density)

Glass masses weighing about 20 g and containing no bubbles were measuredby Archimedes' method to determine the density.

(Strain Temperature)

A strain temperature was measured in accordance with the method asprovided for in JIS R3103-2 (year 2001).

(Transmittance)

A glass substrate having a thickness of 0.5 mm was measured fortransmittance of light at a wavelength of 300 nm by avisible-ultraviolet spectrophotometer.

(T₂)

A rotational viscometer was used to measure the viscosity to determinethe temperature T₂ (° C.) at which the viscosity was 10² dPa·s.

The rotational viscometer was used to measure the viscosity to determinethe temperature T₄ (° C.) at which the viscosity was 10⁴ dPa·s.

(Devitrification Temperature)

As for the devitrification temperature, pulverized glass particles wereput in a platinum-made dish and heat-treated for 17 hours in an electricfurnace controlled at a given temperature, and an average value betweena maximum temperature causing precipitation of a crystal on the surfaceof the glass or inside the glass and a minimum temperature causing noprecipitation of a crystal on the surface of the glass or inside theglass, which were determined by observation with an optical microscopeafter the heat treatment, was employed.

(Devitrification Viscosity)

The rotational viscometer was used to measure the viscosity of moltenglass at a high temperature (1,000° C.-1,600° C.). From the measuredresult, constants of Fulcher's equation were obtained. Thedevitrification viscosity was obtained by the Fulcher's equation usingthe obtained constants.

(Photoelastic Constant)

A measurement was made by a disk compression method (“Measurement ofPhotoelastic Constant of Chemically Strengthened G1ass by DiskCompression Method” by Ryosuke Yokota, Yōgyō Kyōkai-shi, Vol. 87[10](1979), p. 519-522).

Examples 1 to 3 in Table 1 are examples of the invention, and Examples 4to 7 are comparative examples. In an alkali-free glass substrate in eachof Examples 1 to 3, the compaction is 100 ppm or less. Accordingly,pattern deviation hardly occurs. In addition, the values |Δα_(50/100)|,|Δα_(100/200)| and |Δα_(200/300)| are 0.16 ppm/° C. or less.Accordingly, the residual strain generated in the silicon substratetends to decrease in the heat treatment step where the silicon substrateand the glass substrate are laminated to each other.

In a glass substrate in each of Examples 4, 5 and 7, the compaction isout of the range as to the glass substrate according to one of theembodiments of the invention. Accordingly, pattern deviation tends tooccur. In addition, in a glass substrate in each of Examples 4 to 7, thevalues |Δα_(50/100)|, |Δα_(100/200)| and |Δα_(200/300)| are out of theranges as to the glass substrate according to one of the embodiments ofthe invention. Accordingly, the residual strain generated in the siliconsubstrate tends to increases in the heat treatment step where thesilicon substrate and the glass substrate are laminated to each other.

TABLE 1 1 2 3 4 5 6 7 Composition SiO₂ 66.8 66.8 65.6  69.6  66.1 67.168.0 (mol %) Al₂O₃ 13.0 13.0 12.5  12.8  11.2 12.8 11.1 B₂O₃ 4.6 4.69.7  5.9  7.4 1.2 9.1 MgO 8.0 8.0 4.4  1.3 5.4  9.1 2.4 CaO 6.6 6.6 2.0 8.3  4.9 5.4 8.7 SrO 1.0 1.0 5.8  1.4  4.9 4.4 0.6 BaO 0.0 0.0 0.0  0.7 0.0 0.0 0.0 Fe₂O₃ 0.004 0.004  0.004  0.004 0.020 0.020 0.004 Na₂O 0.020.02 0.02 0.02 0.07 0.02 0.02 SnO₂ 0.0 0.0 0.0  0.1  0.0 0.0 0.1 CTE(ppm/° C.) α_(50/100) 2.97 2.91 3.06 3.19 3.38 3.35 3.12 α_(100/200)3.44 3.38 3.36 3.50 3.75 3.82 3.45 α_(200/300) 3.74 3.69 3.61 3.75 4.024.19 3.68 (α_(200/300))/(α_(50/100)) 1.26 1.27 1.18 1.18 1.19 1.25 1.18ΔCTE Δα_(50/100) 0.03 −0.03 0.12 0.25 0.44 0.41 0.17 (ppm/° C.)Δα_(100/200) 0.07 0.01 −0.01  0.13 0.38 0.45 0.08 Δα_(200/300) 0.05 0.00−0.08  0.06 0.33 0.50 −0.01 Δα_(Max) 0.07 0.03 0.12 0.25 0.44 0.50 0.17Expression (1) 3.00 2.95 3.01 3.10 3.37 3.40 3.08 Expression (2) 3.443.38 3.39 3.48 3.78 3.87 3.44 Expression (3) 3.76 3.71 3.65 3.71 4.044.24 3.63 Expression (4) 1.25 1.26 1.22 1.20 1.20 1.25 1.18 Compaction(ppm) 53 1 17    120    120 44 340 BHF haze (%) 15 15 (<1)    0.3  1 481 HF etching rate ((mg/cm²)/min) 0.13 0.13 (0.13) 0.13 0.16 0.17 0.14Young's modulus (GPa) 84 84 75    77    76 85 73 Density (g/cm³) 2.472.47 2.48 2.47 2.52 2.59 2.4 Strain temperature (° C.) 711 711 672   703    670 716 667 Transmittance (%) @300 nm 75 75 75    70    50 50 75(0.5 mmt) T2 (° C.) 1647 1647 1647     (1720)     1645 1654 1692 T4 (°C.) 1295 1295 1284     (1330)     1275 1298 1296 Devitrificationtemperature (° C.) 1305 1305 1295     — 1270 1285 — Devitrificationviscosity 3.9 3.9 4.0  — 4.1 4.1 — Photoelastic constant 29 29 32   30    31 27 34 (nm/cm/MPa) Average cooling rate R (° C./min) 40 1   1230    40 40 680 Evaluation ◯ ◯ ◯ X X X X

TABLE 2 silicon substrate α_(Si50/100) 2.94 ppm/° C. α_(Si100/200) 3.37ppm/° C. α_(Si200/300) 3.69 ppm/° C. α_(Si200/300)/α_(Si50/100) 1.25

The present application is based on Japanese Patent Application No.2016-154682 filed on Aug. 5, 2016, the contents of which areincorporated herein by reference.

The invention is not limited to the aforementioned embodiments, butdeformations, improvements, etc. can be made suitably. In addition,materials, shapes, dimensions, values, forms, numbers, arrangementplaces, etc. of respective constituent elements in the aforementionedembodiments are not limited. Any materials, any shapes, any dimensions,any values, any forms, any numbers, any arrangement places, etc. may beused as long as the invention can be attained.

INDUSTRIAL APPLICABILITY

According to one embodiment of the invention, it is possible to providea glass substrate suitable for manufacturing a small-size andhigh-definition display device. In addition, it is possible to provide asemiconductor device and a display device using the glass substrate.

According to one embodiment of the invention, it is possible to providea glass substrate suitable for manufacturing a display device providedwith a transparent image display element or a reflection displayelement, as a high-definition display device. Examples of such displaydevices may include liquid crystal display devices (LCDs), transparentliquid crystal display devices, LCOSs (Liquid Crystals On Silicon),MEMSs (Micro Electro Mechanical Systems such as digital mirror devices),etc.

According to one embodiment of the invention, it is possible to providea glass substrate suitable for manufacturing a display device providedwith a self-luminous display element using electroluminescence, asanother display device. Examples of such display devices may includeorganic EL display devices, inorganic EL display devices, micro LEDs,etc.

Further, according to an embodiment of the invention, it is possible toprovide a glass substrate suitable for manufacturing a display devicesuch as a head mounted display or a projector.

Moreover, according to an embodiment of the invention, it is possible toprovide a glass substrate suitable for manufacturing a display deviceprovided with a display element having a pixel density (imageresolution) of 1,000 ppi or higher in an element surface of the displayelement, as a high-definition display device.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   10: silicon substrate-   20: bonding layer-   30: thin film transistor-   40: display element-   50: laminated substrate-   52: semiconductor device-   54: display device

1. A glass substrate having a compaction of 0.1 to 100 ppm, and havingthe following composition, as represented by molar percentage based onoxides: SiO₇: 50% to 75%, Al₇O₃: 6% to 16%, B₂O₃: 4% to 15%, MgO: 0% to15%, CaO: 0% to 13%, SrO: 0% to 11%, and BaO: 0% to 9.5%, wherein thecomposition of the glass substrate satisfies:0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ q_(eq)) is 2.70-3.20;0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913×(content of MgO)+0.1621×(content of CaO)+0.1900×(content ofSrO)+0.2180×(content of BaO)+0.0391×(log₁₀ q_(eq)) is 3.13-3.63;0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ q_(eq)) is 3.45-3.95; and0.0111×(content of SiO₂)+0.0250×(content of Al₂O₃)+0.0078×(content ofB₂O₃)+0.0144×(content of MgO)+0.0053×(content of CaO)+0.0052×(content ofSrO)+0.0013×(content of BaO)−0.0041×(log_(i0) q_(eq)) is 1.10-1.30.where the content of SiO₂, the content of Al₂O₃, the content of B₂O₃,the content of MgO, the content of CaO, the content of SrO, and thecontent of BaO are contents of respective components contained in theglass substrate as represented by molar percentage based on oxides, andq_(eq) is an equivalent cooling rate (unit: ° C./min), wherein the glasssubstrate has a BHF haze of 20% or less and a photoelastic constant of33 nm/(MPa·cm) or less, and wherein the glass substrate shows areduction amount ((mg/cm²)/min) per unit area and unit time when theglass substrate is immersed in a 5 mass % hydrofluoric acid watersolution at 25° C. of 0.07 (mg/cm²)/min or more and 0.18 (mg/cm²)/min orless.
 2. The glass substrate according to claim 1, wherein an averagecoefficient of thermal expansion α_(50/100) at 50° C. to 100° C. is from2.70 ppm/° C. to 3.20 ppm/° C.
 3. The glass substrate according to claim1, wherein an average coefficient of thermal expansion α_(200/300) at200° C. to 300° C. is from 3.45 ppm/° C. to 3.95 ppm/° C.
 4. The glasssubstrate according to claim 1, having a value α_(200/300)/α_(50/100)obtained by dividing an average coefficient of thermal expansionα_(200/300) at 200° C. to 300° C. by an average coefficient of thermalexpansion α_(50/100) at 50° C. to 100° C. of from 1.10 to 1.30. 5.(canceled)
 6. The glass substrate according to claim 1, wherein anaverage coefficient of thermal expansion α_(200/300) at 200° C. to 300°C. is from 3.55 ppm/° C. to 3.85 ppm/° C.
 7. The glass substrateaccording to claim 1, wherein the content of B₂O₃, as represented bymolar percentage based on oxides, is 9.7% to 15%.
 8. The glass substrateaccording to claim 1, having a total content of CaO, SrO, and BaO of 5%or higher, satisfying a relation of (content of Al₂O₃)≥(content of MgO),and having a devitrification viscosity of 10^(3.8) dPa·s or higher. 9.The glass substrate according to claim 1, wherein an average coefficientof thermal expansion α_(100/200) at 100° C. to 200° C. is from 3.13ppm/° C. to 3.63 ppm/° C.,
 10. The glass substrate according to claim 1,wherein the composition of the glass substrate satisfies:0.0177×(content of SiO₂)−0.0173×(content of Al₂O₃)+0.0377×(content ofB₂O₃)+0.0771×(content of MgO)+0.1543×(content of CaO)+0.1808×(content ofSrO)+0.2082×(content of BaO)+0.0344×(log₁₀ q_(eq)) is 2.80 to 3.10;0.0181×(content of SiO₂)+0.0004×(content of Al₂O₃)+0.0387×(content ofB₂O₃)+0.0913 ×(content of MgO)+0.1621×(content of CaO)+0.1900×(contentof SrO)+0.2180×(content of BaO)+0.0391×(log₁₀ q_(eq)) is 3.23 to 3.53;0.0177×(content of SiO₂)+0.0195×(content of Al₂O₃)+0.0323×(content ofB₂O₃)+0.1015×(content of MgO)+0.1686×(content of CaO)+0.1990×(content ofSrO)+0.2179×(content of BaO)+0.0312×(log₁₀ g_(eq)) is 3.55 to 3.85; and0.0111×(content of SiO₂)+0.0250×(content of Al₂O₃)+0.0078×(content ofB₂O₃)+0.0144×(content of MgO)+0.0053×(content of CaO)+0.0052×(content ofSrO)+0.0013 ×(content of BaO)−0.0041×(log₁₀ q_(eq)) is 1.20 to 1.27.11-13. (canceled)
 14. A semiconductor device comprising the glasssubstrate according to claim 1, and a thin film transistor having acrystalline silicon film formed on the glass substrate.
 15. Thesemiconductor device according to claim 14, wherein the crystallinesilicon film is a single-crystal silicon film.
 16. A display devicecomprising the semiconductor device according to claim 14 and a displayelement.
 17. The display device according to claim 16, wherein thedisplay element is a transparent image display element or a reflectionimage display element.
 18. The display device according to claim 16,wherein the display element is a self-luminous display element usingelectroluminescence.
 19. The display device according to claim 16, whichis a head mounted display or a projector.
 20. The display deviceaccording to claim 16, having a pixel density (image resolution) in anelement surface of the display element of 1,000 ppi or higher.
 21. Thesubstrate according to claim 1, having a total content of Li₂O, Na₂O,and K₂O of 0% to 0.1%.
 22. The substrate according to claim 21, whereinthe content of Al₂O₃ is 11% to 16%.
 23. The substrate according to claim22, wherein the content of CaO is 0% to 8%.